Exchange operator tells lawmakers that the move would reduce risk in the $13.9 trillion U.S. Treasury market

WASHINGTON—Exchange operator Nasdaq Inc. told lawmakers Friday that systemic risk in the $13.9 trillion U.S. Treasury market would be reduced by requiring trades be guaranteed by clearinghouses.

Regulators required more extensive use of central clearing for such financial derivatives as interest-rate swaps after the 2008 financial crisis. But the vast majority of secondary-market trading in U.S. Treasurys doesn’t involve a central clearinghouse, as many electronic trading firms that are major players in the market find it...